It opens with children hearing the legend of the evil merwitch sisters destroying Atlantis. It closes with shipmates singing of coconuts and mangoes under the moon. In between, The Unsinkable Walker Bean rollicks its way across an ocean as a young stowaway tangles with pirates, thieves, friends, foes and supernatural bad vibes.

That’s right, I said rollicks.

And you know it’s good, because it’s the kind of book — graphic novel, this is — that has a map of its world in the front pages. “The Known World of Walker Bean” vaguely but not exactly resembles the layout of continents as we know them; it has an Atlantic Ocean but also a Grand Ocean, an Orient Ocean, and places like Subrosa Sound and Winooski Bay.

That last is a nod to Vermont, from where hails colorist Alec Longstreth — he lives in White River Junction and teaches at the Center for Cartoon Studies there.

A note at the end says, “Using some old, faded children’s books for inspiration, Aaron and Alec created a custom palette of 75 colors, which are the only colors in this book. … it makes the colors feel very unified.” It’s a warm and rich palette, lending an air of fireside coziness to go along with the tale’s adventure-driven excitement. For Walker Bean is a tender young lad, ready for adventure but not immune to homesickness.

In his world, everyone knows the legend of the merwitch sisters; now Walker’s intrepid grandfather claims to have found their lair in an ocean trench near the Mango Islands. Grandpa lays dying, his strength sapped from the evil powers of a mysterious bag that contains the merwitches’ secrets. Unless Walker returns that bag (“PROMISE me you won’t look in the bag”) to the merwitches’ trench, and quick, good old granddad will perish and Winooski Bay will be destroyed.

See, granddad, an old-school inventor/explorer, had originally thought that knowing the merwitches’ secrets would be worth a little suffering. He was greedy. Now, of course, he knows better.

So Walker takes the bag and runs with it, dodging the bad guys who want it to make them rich.

And it’s pretty much rollicking from there on out. I won’t spoil the details for you. There is the promise of a sequel.

The story is not perfectly smooth; there are a few points that feel a little contrived, a little too much, for me, and somehow not all the characters go together that well — I feel like some of them belong in a different story or need to be brought more fully into this one. But this is not enough to get in the way of a generally good time. Overall it’s a pretty good comic book, colorful (in both ways) and absorbing, worth a stack of Saltines and a jar of peanut butter on a porch on a hot summer day. I like Walker, who bonds with his grandfather and grows up before our eyes, rising to occasions in rather realistic, if impressively inventive, ways. The merwitches in this installment are frankly kind of weird, but I’ll be keeping my eyes out for more of Walker Bean.